In the field of optical devices, such as, displays, light emitting diodes and solar cells, various proposals have been recently made for the purposes of energy conservation and of improvement in light utilization efficiency. For example, there is a known method for increasing the aperture ratio of a liquid crystal display. In that method, a transparent planarization film is formed to cover a thin-film transistor (hereinafter, often referred to as “TFT”) element and then pixel electrodes are formed on the planarization film (see, Patent document 1). Similarly to this method for a liquid crystal display, there is also a method proposed in order to increase the aperture ratio of an organic electric field light-emitting device (hereinafter, often referred to as “organic EL device”). In the proposed method, the constitution of the device is changed from a type in which a light-emitting layer is formed by deposition on transparent pixel electrodes provided on a substrate so that the emitted light is extracted from the substrate side (i.e., bottom emission type) to another type in which a TFT element, a planarization film formed thereon to cover the TFT element, transparent pixel electrodes provided thereon, and a light-emitting layer formed thereon are so laminated that the light given off from the light-emitting layer is extracted from the side opposite to the TFT element (i.e., top emission type) (see, Patent document 2).
According as new technologies such as 3D displaying have been introduced to meet increasing needs for improvement of displays in resolution, in upsizing and in image quality, signal delay on the wiring has been becoming a problem. Specifically, the speed of rewriting image information (i.e., frame frequency) has been accelerated, and accordingly the input time of signals into the TFT element has been shortened. However, even if it is attempted to improve the response speed by broadening the wiring width to reduce the wiring resistance, the broadening of the wiring width is limited by the requirements of high resolution displaying and the like. In view of that, it is proposed to increase the wiring thickness so as to solve the problem of signal delay (see, Non-patent document 1).
As one of the materials for the planarization film formed on a TFT substrate, it is known to adopt a negative-working photosensitive composition mainly comprising a polysiloxane compound and a polymerization initiator. The polysiloxane compound is obtained by polymerization of a bifunctional group-containing silane compound, such as, dialkyldialkoxysilane, in the presence of catalysis. The composition is generally coat on a substrate to form a coating, which is then exposed to light, developed and heated to produce a planarization film. During the exposure to light, the composition undergoes polymerization reaction to cure but is not completely cured. It is, therefore, general that the coating is further heated after exposed to light so as to promote the polymerization reaction (post-exposure baking step) and thereafter developed. However, in view of the production efficiency, the above process is disadvantageous because it requires the heating step and consumes costly energy for heating.